1. Field of the Invention
The present invention relates to a single crystal pulling method for producing a single crystal of a semiconductor such as silicon (Si) or gallium arsenide (GaAs) using a continuous charge magnetic field application CZ technique.
2. Description of the Related Art
Single crystal pulling apparatuses employing the CZ technique comprise a gas tight chamber, a crucible for storing a semiconductor melt which is positioned inside the chamber, a heater for heating the semiconductor melt, and a pulling mechanism for pulling a single crystal of the semiconductor while being rotated. In this type of apparatus a single crystal seed crystal of the semiconductor is immersed in the semiconductor melt inside the crucible, and the seed crystal is then gradually pulled upwards, growing a large diameter single crystal of the semiconductor which has the same orientation as the seed crystal.
In recent years there has been considerable development of the continuous charge magnetic field application CZ technique (hereafter abbreviated as the CMCZ technique), which is a variety of the CZ technique where the pulling operation is conducted during continuous supply of the source material to the crucible. In the CMCZ technique a double crucible comprising an outer crucible and an inner crucible comprised of a cylindrical partitioning body is employed, and a single crystal of the semiconductor is pulled from the inner crucible while source material is added to the outer crucible through a source material supply tube made of quartz, and moreover, convection currents within the semiconductor melt inside the inner crucible are suppressed by applying an external magnetic field to the semiconductor melt. The quartz source material supply tube is suspended from the upper portion of the chamber and the lower end opening of the tube is proximate to the surface of the semiconductor melt inside the outer crucible.
The lower end opening of the source material supply tube sits several centimeters above the surface of the semiconductor melt, while the source material is stored in the top portion of the chamber to avoid exposure to radiated heat from the heater and the semiconductor melt. Furthermore, the source material injected into the source material supply tube, flows down the inside of the source material supply tube towards the inside of the chamber, along with the inert gas such as argon which is being used, and enters the semiconductor melt from the aforementioned lower end opening of the tube.
However, in current single crystal pulling apparatuses which employ CMCZ single crystal pulling techniques or vapor techniques, there is a tendency, depending on operating conditions, for the frequency of the occurrence of voids (a lattice defect) in the crystal lattice of the pulled single crystal to be larger than that observed with normal CZ techniques and apparatus.
It is considered that an increase in the frequency of the occurrence of voids in single crystals grown by the CMCZ technique is related to the technique employed for adding source material from the source material supply tube. That is, because the source material is added together with the inert gas flowing through the source material supply tube into a chamber which is maintained at a predetermined pressure, it can be estimated that there is a relationship between the flow rate of the inert gas and the pressure in the furnace, and the occurrence of voids.
The present invention takes the above situation into consideration, with the object of providing a single crystal pulling method which enables a reduction in the occurrence of voids, and an apparatus in which the method is employed.